Area forecast discussion
National Weather Service Bismarck ND
618 PM CDT Wednesday Jun 19 2013
Update...
issued at 618 PM CDT Wednesday Jun 19 2013
Current satellite imagery shows a middle level shortwave rotating
near shields in Sioux County with radar continuing to indicate an
area of showers and isolated thunderstorms with this wave. Nothing
severe as of yet with weak shear...surface to 6km shear values well
less than 30kt. Thus despite high reflectivity's low to middle
levels...they have not been able to reach much higher to produce severe
criteria. Have adjusted hourly temperatures in this area with
cooler readings over the next few hours. This shortwave will
continue to move northeast into the southern James River Valley
but not expecting anything severe with it. An isolated
thunderstorm was also noted just southeast of Kenmare moving
northwest and will continue to monitor it.
Further west...strong southeasterly low level flow and strong
southwest wind aloft are resulting in surface to 6km shear values of
40kt in far southwest North Dakota. Surface map and satellite imagery
depict a warm front in central South Dakota with a small cumulus
field southwest...and in northwest North Dakota. This will be
watched closely this evening for thunderstorm development. The
12z WRF did pick up on the Sioux County convection mentioned above
for this evening...and it indicates that a line of convection
will form in eastern Montana and western North Dakota shortly
after 00z. The hrrr and rap delay the line until around 06z...and
then ramp up convection in northwest North Dakota thereafter. Additional
convection is foreacst to initiate and extend into the James River
Valley after 06z...essentially resulting in a northwest to
southeast convection line along the warm frontal boundary.
For this evening...any area is prone to convection...and will
continuously monitor for initial signs. However more confident
with severe weather development west and northwest...with better
shear values and closer to shortwave energy ejecting from Idaho
into Montana through most of the night. This remains in line with
the current forecast and Storm Prediction Center day one outlook. Minimal changes to
current evening/overnight forecast. Wind Advisory continues in the
southwest through early evening.
&&
Short term...(this evening through thursday)
issued at 333 PM CDT Wednesday Jun 19 2013
Main concerns this forecast include thunderstorms...their severe
potential and possible heavy rain. Late this afternoon an
elevated mixed layer from eastern Montana into western North
Dakota is providing a significant cap. To the east of this a
moisture plume extends from eastern North Dakota through the
north central supporting weak convection but with little wind shear
to support continuing development. So will be waiting for the
a stronger shortwave across Wyoming and Montana to enter the
picture later this evening and overnight. This will support more
widespread thunderstorms...and current thinking is a line of
storms capable of severe winds may develop across Montana and
enter the northwest into portions of the north central late
evening or after midnight. Above normal moisture is available...
with precipitable waters significantly above normal suggesting that heavy rain
is possible. The one factor limiting flash flood producing rains
may be the expected fast movement of the thunderstorms.
On Thursday...the expected remnants of overnight convection will
be in central North Dakota. Another round of severe storms expected
to pick up steam late in the afternoon and evening.
Long term...(thursday night through wednesday)
issued at 333 PM CDT Wednesday Jun 19 2013
The main forecast concerns in the long term period are severe
weather potential...heavy rain potential...and timing issues through
Saturday. The upper level low/trough remains in place over The
Rockies through Saturday...then the models begin to move the upper
low northeastward towards southern Saskatchewan/Manitoba
Saturday/Saturday night/Sunday. Chance of showers and thunderstorms
into early next week with general southwest upper level flow.
Thursday...strong to potentially severe storms from an organized
storm cluster may persist across northern counties Thursday
morning...and storm re-intensification is expected during the
afternoon/evening hours along a strong moisture convergence axis
with dewpoints in the upper 60s and precipitable water values approaching 2
inches. By early Thursday evening the NAM and GFS are in agreement
regarding the position of the surface trough...roughly from near
Bottineau/Minot to between Bismarck and Jamestown. The European
model is a bit slower...depicting the front from near Stanley to
near Bismarck. Felt confident enough that the far southwest corner
of the state would be free of thunderstorms Thursday evening...and
kept best chances of thunderstorms from the Bottineau/Turtle
Mountains to Steele and the James River Valley with "likely"
chances. Severe parameters continue along and east of the front.
Cape values up to 2500 with 0-6km bulk shear values up to 40-45.
By midnight/1am (06z fri)...the GFS is fastest - depicting the front
over the Red River valley - and the NAM/ec keep it in or just east
of the James River Valley. Regardless...chances of precipitation
fall in central North Dakota with the surface front exiting the area
and upper level support weakening. However another upper level
impulse approaches southwestern North Dakota from Wyoming. Bulk
shear increases with moderate increases in cape...and kept a slight
chance in the west.
For Friday...today's models did not set up a heavy rain
event...instead several upper level impulses move through the state
on the southwest flow aloft...but the models develop the surface low
farther south in the Southern Plains. Kept good chances of
precipitation for Friday and Friday night. Severe parameters still
in place.
Saturday the models develop the surface low farther north with the
upper level low/trough moving northeastward across Montana into
western North Dakota and into southeast Saskatchewan. This would set
up a widespread moderate to heavy rain event...but models are not in
agreement for placement and timing.
Near seasonal temperatures are expected through the weekend...followed by
some warming early next week. Highs 70-80 through the weekend...and
low to middle 80s early next week.
&&
Aviation...(for the 00z tafs through 00z Thursday evening)
issued at 618 CDT Wednesday Jun 19 2013
Mainly VFR ceilings/visibilities through 06z Thursday...with an increasing
threat for showers and thunderstorms west overnight and central
Thursday. With any heavy thunderstorms...expect brief periods of
MVFR cigs/vsbys. Predominant showers and thunderstorms have been
to the 00z forecasts late Wednesday night through Thursday.
&&
Hydrology...
issued at 333 PM CDT Wednesday Jun 19 2013
The threat for heavy rain exists with the expected thunderstorms
late tonight...Thursday...Thursday night and Friday. The precipitable
water (pwat) is much above normal for this time of year. If
thunderstorms form as expected...the best chance for an inch or
more of rainfall will be from far northwest...north central
through the northern James River Valley. One to two inches of
rain in this two day period is possible with multiple lines of
thunderstorms. The one factor that may limit the flash flood
potential will be significant movement of the storms. Also the
surface moisture...while being high...has had some time o dry out
recently. Rainfall amounts of one to 2 inches should be able to be
absorbed...although more than two inches would likely cause some
problems.
&&
Bis watches/warnings/advisories...
Wind Advisory until 9 PM MDT this evening for ndz031>033-040-041-
043-044.
&&
$$
Update...Kansas
short term...warm air advection
long term...jv
aviation...Kansas
hydrology...warm air advection
